Biol 3320 Cell Biology Lecture Notes PDF

8/29/2024 2024/08/29 Thursday Biol 3320 Cell Biology CRN 13746 Protein structure & function (II) 1...

8/29/2024 2024/08/29 Thursday Biol 3320 Cell Biology CRN 13746 Protein structure & function (II) 1 1 The 20 amino acids commonly found in proteins *The 3-letter abbreviation for each aa 2 Fig. 3 - 2 2 1  8/29/2024 The nine essential amino acids They cannot be synthesized by human cells and so must be supplied in the diet 3 Fig. 2 - 61 3 Proteins are polymers of amino acid residues linked together by peptide bonds Each aa contributed 3 bonds to the backbone of the chain 4 Fig. 3 - 1 4 2  8/29/2024 Proteins are made of polypeptide backbone with attached side chains Steric limitations on the bond angles in a polypeptide chain The peptide bond is planar and does not permit rotation Fig. 3 - 3 5 5 Steric limitations on the bond angles in a polypeptide chain By contrast, rotations can occur about the Cα- C bond and about the N- Cα bond R groups bonded to the α‐carbon rotate freely, giving it the mobility to interact with other molecules (e.g., water, other parts of the protein, etc.) in 3‐D Fig. 3 - 3 6 6 3  8/29/2024 Terminology 1. A polymer of a few amino acids (2 - about 50) is a peptide 2. A single chain (one free amino and one free carboxyl) of longer polymer is a polypeptide 3. Proteins may have one or more polypeptide chains. For proteins containing multiple polypeptides (=multimeric proteins), each polypeptide is called a subunit 4. Subunits may be held together by noncovalent bonds (common) or by covalent bonds (less common) 7 7 III. Protein Folding 8 8 4  8/29/2024 Disulfide bonds (as an example of covalent bonds) Disulfide bonds form between adjacent cysteine side chains to join either two parts of the same polypeptide chain or two different polypeptide chains 9 Fig 3 - 25 9 Three types of noncovalent bonds help proteins fold Ionic bonds (salt bridges) Hydrogen bonds (H-bonds) Van der Waals Interactions Fig. 3 - 4 10 10 5  8/29/2024 The most common hydrogen bonds in cells 11 Fig. 2 - 3 11 Van der Waals Forces (attractions) 12 Panel 2 - 3 12 6  8/29/2024 Van der Waals Forces (attractions) 13 Panel 2 - 3 13 Table 2-1 Noncovalent chemical bonds have